Concussion not the only problem in football: New study shows that even routine hits can cause structural damage to brain
Concussions are not the only cause of damage to the brain in contact sports.
A study of college football players shows that typical hits to the head sustained from playing just one season cause damage to the brain.
Using sensors in helmets and MRI scans of college football players, the research team from Carnegie Mellon University and the University of Rochester Medical Center found that these everyday hits cause structural changes to the brain.
Public perception is that the big hits are the only ones that matter.
However, the research team says, with a focus on the big hits, the public is missing what is likely causing the long-term damage in players’ brains. It is not just the concussions, everyday hits do so too.
“For good reason, there has been an emphasis on concussion, and there has been an emphasis on the big hits that everybody notices. What our study indicates is that that’s just the tip of the iceberg. There are all of the other hits that players sustain in the course of playing a typical game of football without concussion. And all of those sub-concussive hits seem to add up to cause damage to the brain that we can measure with MRI,” says Brad Mahon, an associate professor of psychology at Carnegie Mellon University and scientific director of the Program for Translational Brain Mapping at the University of Rochester.
The researchers studied 38 players on the University of Rochester football team (National Collegiate Athletic Association (NCAA) Division III).
They placed accelerometers—devices that can measure accelerative force—in their helmets for every practice and game.
The study, published in Science Advances, is part of the newly launched Open Brain Project, a platform to explore the human brain and how it responds to and recovers from injury.
Each player in the study received an MRI scan within two weeks of the start of each season and within one week in the end. The team examined the midbrain white matter of players before and after a college football season. They also measured the magnitude, location, and direction of hits experienced on the field.
The researchers found that all the players sustained repetitive head impacts across the season, but only two of the 38 suffered a concussion.
The midbrain, located in the center of the head and just beneath the cerebral cortex, is part of a larger stalk-like rigid structure that includes the brain stem and thalamus.
The midbrain supports functions like eye movements, which are impacted by concussions and hits to the head.
While head hits are known to affect many parts of the brain simultaneously, the researchers decided to focus their study on the midbrain.
They hypothesized and found that the midbrain is a crucial structure that can serve as an indicator of injury in both concussions and repetitive head hits.
The study found reduced white matter integrity in the midbrain after the season in the players, despite the fact that only two suffered concussions.
The results indicate that repeated, sub-concussive head hits sustained by players over the course of a routine football game can cumulatively cause brain trauma.
“Even without a concussion, the hits players are taking in practice and games appear to cause brain damage over time,” says the study.
The researchers say what they have cataloged are “clinically silent” brain injuries—which cannot be observed simply by looking at or behaviorally testing a player, on or off the field. This, says the team, suggests that catching an injury before it manifests as overt signs and symptoms will prove critical in protecting players from long-term “neurologic injury.”
“The helmet accelerometers measured linear and rotational acceleration during all practices and games, recording all contact that produced forces of 10 gs or greater. Astronauts on the space shuttle experience three gs during lift-off. Race car drivers feel the effects of 6 gs, and car crashes can produce brief forces of more than 100 gs. A total of 19,128 head impacts (hits) were sustained across 38 players. Of those hits, the median force was around 25 gs, with half of the hits exceeding that amount. Only two of these hits resulted in concussions,” says the study.
Of all the hits, 59% (11,334) were sustained in practice and 37% (7022) in competition.
It further says, “While only two players suffered clinically diagnosed concussions during the time they were followed in the study, the comparison of the post- and pre-season MRIs showed that greater than two-thirds of the players experienced a decrease in the structural integrity of their brain. Specifically, we found reduced white matter integrity in the midbrain after the season as compared to before the season. Indicating the injury was specifically related to playing football, we found the amount of white matter damage was correlated with the number of hits to the head players sustained.”
The researchers explain that rotational acceleration (impact causing the head to twist) more so than linear acceleration (head-on impact) is correlated with the observed changes in the structural integrity of white matter in the midbrain.
“The twisting aspect of the force is what is more correlated with the changes that we are observing in these players versus the direct hits. It makes sense because this part of the brain has, what we call biomechanical susceptibility because it is narrow. That predisposes it to twisting,” says Adnan Hirad, an MD/Ph.D. candidate at the University of Rochester’s Medical Scientist Training Program.
The team explains that the brain accumulates a whole variety of toxic, poisonous proteins.
“When those nerve cells break after each head hit, it’s almost like garbage builds up the brain. The brain has a system for getting rid of that. But if it is overwhelmed because it is getting hit 70-80-90 times a day, those proteins just build up,” says study co-author Jeffrey Bazarian, professor of Emergency Medicine, Neurology, Neurosurgery and Public Health Sciences at the University of Rochester Medical Center.
The researchers also conducted a second study.
This group included 29 athletes from various other contact sports who had a clinically defined concussion and 58 who did not.
The concussed participants underwent MRI scans and offered blood samples within 72 hours of injury.
Like the football cohort, those players exhibited reduced structural integrity in the midbrain.
“Besides, they exhibited increased tau, a protein, in their blood. As structural integrity in the brain decreases, tau increases. Tau is an important marker of acute changes in the brain and is thought to be, in the long term, implicated in neurodegenerative diseases,” say the findings.
Although the build-up of tau protein in the midbrain is already associated with neurodegenerative diseases, it was known till now whether structural changes to the midbrain occur during repetitive head impacts that fall short of the clinical diagnosis for concussion
According to the researchers, going forward, if experts want to develop metrics to be able to document and predict the injury burden of contact sports in the absence of concussion, they believe that this part of the brain—the midbrain—is the place to look.
“Our research, in the context of prior research over the past several years, is beginning to indicate that the accumulation of many sub-concussive hits is instrumental in driving long-term damage in football players’ brains. Future research will be required to translate our findings into concrete directives that are relevant to public health. An important direction for future research will be to carry out larger-scale longitudinal studies of contact sports athletes in various ages groups,” says the team.